Bartonella henselae invades human mesenchymal stromal cells inducing a neovascularitazion process

Introduction. B. henselae is the etiologic agent of Cat-scratch disease (CSD), a self‐limiting chronic lymphadenopathy, in immunocompetent humans, mainly related to a cat scratch or bite. Instead, in immunocompromised patients B. henselae can cause bacillary peliosis hepatis angiomatosis. Endothelial cell (ECs) infection represents an important step in the pathogenesis of cat scratch disease and bacillary angiomatosis. In addition to ECs, bartonella also has a tropism for other cell types including cells of mononuclear phagocytes lineages. The cell types in which bartonella defend themselves from immune system have been considered as niches that could periodically seed bacteria into the bloodstream. This could explain the dissemination of B. henselae in the complication of CSD and the bacteraemic relapses that characterize the infection. However many aspects related to intracellular persistence of bartonella are still unclear and the presence of yet unrecognized niche has been hypothesized. Mesenchymal stem cells (MSCs) are multipotent adult stem cells that are present in multiple tissues, including bone marrow and adipose tissue. MSCs can differentiate into various cell lineages and have a proven ability to augment the neovascularization processes. The purpose of this study was to characterize the interaction of B. henselae with MSCs. Materials and methods. Human adipocyte-derived mesenchymal stromal cells (Ad-MSCs) were stimulated with MOI 100 of B. henselae for 48-96 hr and 7 days. Different cytokines and chemokines upon B. henselae infection were measured by ELISA kits. The internalization of bacteria in Ad-MSCs was demonstrated by immunohistochemical and immunofluorescence analysis and by gentamicin protection assay. Cells were also evaluated by RT-PCR and FACS analysis for the expression of TLR-2/TLR-4 after B. henselae stimulation. Moreover, through preparation of conditioned medium from B. henselae-infected MSCs, we evaluated the capacity of MSCs to modulate angiogenesis. Results. Infection of Ad-MSCs with B. henselae resulted in an increase of VEGF, CXCL8, IL-6, IP-10, CCL5 and PDGF-D secretion in a time-dependent manner. B. henselae can augment TLR-2 expression as demonstrated by RT-PCR and FACS analysis. Bacteria can enter the intracellular space of MSCs and can be detected as solitary bacteria in the perinuclear area and in clusters inside vacuolic compartments after 96 hr of infection. Moreover bacteria persist at 7 days post infection, as demonstrated by immunofluorescence. Finally the conditioned medium of infected MSCs can efficiently promote endothelial cells angiogenesis. Discussion and Conclusions. We demonstrate that B. henselae invades and persist in MSCs. MSC infection triggers the production of pro-angiogenic factors that promote endothelial cells proliferation and capillary tube formation indicating that MSCs could represent a potential habitat of B. henselae and create a proangiogenic microenviroment typical of this bacterial infection.